JPH0686221B2 - Electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric motor type power steering apparatus provided with an electric motor for generating a steering assist force in a steering force transmission system, and more specifically, to a transmission system electric motor or The present invention relates to an electric motor type power steering apparatus that limits a current value to be applied to an electric motor according to the temperature of a mechanical element or the like.

(Prior Art) Generally, in an electric motor type power steering apparatus having an electric motor for generating a steering assist force in a steering force transmission system, a steering speed of a steering wheel, a steering angle, a steering force or a vehicle speed of a vehicle. Controls the value of the current supplied to the electric motor according to steering information such as
The steering assist force generated by the electric motor is transmitted to the steered wheels via the gear mechanism of the transmission system and the like together with the manual steering force applied to the steering wheel to reduce the steering burden on the driver.

However, such an electric motor type power steering apparatus has a heat generating element such as a winding and a rectifying part of an electric motor, a power transistor for driving the electric motor, and a sliding part of a mechanical part such as a reduction gear in a transmission system, and The device itself is arranged in the vicinity of a heating element such as an engine, and the ambient temperature also changes according to the four seasons. Therefore, in such an electric power steering apparatus, temperature fluctuations around the electric motor, the power transistor for driving, or the mechanical portion are notable, and the temperature is inevitably high. Such an electric motor-driven power steering device is naturally designed to withstand components such as electric motors even in high temperature environments, but under unusual operating conditions, the operating limits of the components are limited. In some cases, it was unavoidable to use in a high temperature environment that exceeds the temperature.

Therefore, in the past, an electric motor-powered steering device for the purpose of protecting equipment in such a high temperature environment has been developed in actual use.
It is proposed in Japanese Patent Publication No. 65. This electric motor type power steering apparatus protects the electric motor and the like by limiting the electric current supplied to the electric motor when the temperature of the electric motor exceeds a predetermined temperature.

(Problems to be Solved by the Present Invention) However, in the electric motor type power steering apparatus described in Japanese Utility Model Laid-Open No. 61-91465, when the temperature of the electric motor exceeds a predetermined temperature, Regardless of the current, the current supplied to the electric motor is limited, so that the steering assist force generated by the electric motor when the electric motor is hot becomes small regardless of the steering force applied to the transmission system, which deteriorates the steering feeling. There was a problem.

The present invention has been made in view of the above-mentioned problems, and provides an electric motor type power steering apparatus that controls a current supplied to an electric motor based on a steering force corrected by a temperature of a steering system, and a steering feeling. The purpose is to protect equipment such as electric motors without deteriorating.

(Means for Solving Problems) The present invention, as shown in the overall configuration diagram of FIG. 1, includes a motor for generating a steering assist force in a steering force transmission system,
In the electric power steering apparatus, the electric current supplied to the electric motor is controlled based on output signals of at least steering force detecting means for detecting a steering force of the transmission system and temperature detecting means for detecting a temperature of the transmission system. A correction unit that corrects the steering force detected by the steering force detection unit based on the temperature detected by the temperature detection unit to determine a corrected steering force, and at least a high temperature based on the corrected steering force determined by the correction unit. Sometimes a current value determining means for determining a target current value for which an auxiliary force corresponding to the frictional resistance component of the transmission system is secured, and a current of the target current value to the electric motor based on an output signal of the current value determining means. The gist is to provide an energizing means for energizing.

(Effect) According to the electric motor type power steering apparatus of the present invention, the current supplied to the electric motor is controlled based on the corrected steering force corrected by the temperature of the electric transmission system such as the electric motor or the mechanical portion to control the temperature of the electric transmission system. When is high, the energizing current to the electric motor is reduced, so the amount of heat generated by the electric motor and the like is also reduced, and the temperature does not rise above the operating limit temperature. The electric current supplied to the electric motor is corrected by the temperature of the transmission system, but is basically controlled based on the steering force (steering reaction force) of the transmission system, and the friction (friction) component of the transmission system is obtained. Since the control is performed so as to secure a corresponding auxiliary force, the steering feeling does not deteriorate, and steering such as emergency avoidance can be reliably performed.

(Example) Hereinafter, an example of the present invention is described based on an accompanying drawing.

2 to 7 show an electric motor type power steering apparatus according to one embodiment of the present invention. FIG. 2 is a sectional view of a mechanical portion, and FIG.
Fig. 2 is a sectional view taken along the line III-III in Fig. 2, and Fig. 4 is IV in Fig. 2.
-IV arrow sectional view, FIG. 5 is a VV arrow sectional view of FIG. 2,
FIG. 6 is an electric circuit diagram, and FIGS. 7 and 8 are flowcharts.

In FIG. 2, (11) is a pinion shaft connected to a steering handle (not shown) via a steering shaft or the like, and this pinion shaft (11) is provided with bearings (12) and (13). ) Is rotatably supported. The rotation center of the pinion holder (14) is the pinion shaft (11).
It is eccentric with respect to the rotation center of and is rotatably supported by the rack case (17) by bearings (15) and (16). A pinion gear (11a) is fixed to the pinion shaft (11), and the pinion gear (11a) meshes with rack teeth (20a) formed on the back side of the rack shaft (20) in the figure.

A steering torque sensor (steering force detection means) (21) and a control circuit (63) are provided above the case (17) around the pinion shaft (11), and a drive circuit (see FIG. 65) is provided. The steering torque sensor (21)
As shown in FIG. 3, the pinion holder (14) is composed of a movable core (14a) protruding from the upper surface and a differential transformer (22) fixed in the case (17). The differential transformer (22) includes a primary coil (24), two secondary coils (25), and an E-shaped iron core (23) fixed to the case (17).
A compensation tertiary coil (not shown) is wound around the (25) and the primary coil (24) so that the steering torque, that is, the steering reaction force acting on the steering wheel is displaced by the displacement of the movable core (14a). Detect with. In this steering torque sensor (21), an AC pulse signal from the control circuit (63) is applied to the primary coil (24), and the secondary coils (25) and (25) follow the rotation of the pinion holder (14). The steering torque detection signals (S ₁ ) and (S ₂ ) are differentially output to the control circuit (63) corresponding to the relative displacement with the movable core (14a). In FIG. 2, (27) is a seal member, (28) is a cap, and (29) is a power cord connected to a battery power source.

Both ends of the rack shaft (20) are connected to steering wheels (not shown) through tie rods and the like, and the pinion gear (11
via a rack guide (not shown) near a),
It is axially movably supported by a case (17) via a metal bearing (31) on the left side in the figure.

Further, in the case (17), an electric motor (5) that generates a steering assist force is provided around the center of the rack shaft (20). The electric motor (5) includes a field magnet (33) fixed to an inner peripheral surface of a rack case (17), a rotor (34) rotatably arranged around a rack shaft (20), and a rack case. A commutator (36) housed in a holder (35) fixed to (17), and a brush (37) slidingly contacting the commutator (36).
And have. The rotor (34) has bearings (38), (39)
A cylindrical shaft (40) that is rotatably supported by and functions as an output shaft, and a laminated iron core (41) having a skew groove on the outer periphery of the cylindrical shaft (40) and a multi-turned armature winding ( 42) is coaxially and integrally fixed. The armature winding (42) is connected to a later-described electric motor drive circuit (65) of the control device (62) via the commutator (36) and the brush (37), and is drive-controlled by the control circuit (63). .

Near the electric motor (5), a temperature sensor (temperature detecting means) connected to the control circuit (63) on the inner wall of the case (17).
(60) is provided. This temperature sensor (60) is composed of a thermistor whose resistance value changes according to temperature change,
A temperature detection signal (S ₃ ) having a voltage characteristic that is substantially inversely proportional to the temperature change is output to the control circuit (63). Needless to say, the temperature sensor (60) may be replaced with one having an equivalent function such as a thermocouple.

Further, in the case (17), a speed reducer (46) including gears (40a), (43), (44) and (45) is provided on the left side of the electric motor (5) in the figure. . This reduction gear (4
6), as shown in FIG. 4, the gear (40a) is the cylinder shaft (40).
It is formed on the outer circumference of this gear (40a) and has a small diameter gear (43)
Mesh with each other, and the small diameter gear (44) integrally connected to the gear (43) meshes with the large diameter gear (45) fixed to the screw shaft (48). As shown in FIG. 2, the screw shaft (48) is mounted in the rack case (17) in parallel with the bearing shaft (4).
9), (50) are rotatably supported by the rack shaft (2
0) spiral groove (4
8a) has been formed. As shown in FIG. 5, a nut member (52) having a spiral groove (52a) formed on its inner peripheral surface is fitted to the screw shaft (48) through a large number of balls (not shown). The spiral grooves (48a), (52a) and the balls constitute a well-known ball screw mechanism (53), and the ball screw mechanism (53) causes the screw shaft (48) and the nut member (52).
And are connected so that power can be transmitted.

The nut member (52) has a pair of flanges (54), (54), and the flanges (54), (54) pass through the bushes (55), (55), respectively, and the bolts (56), (56)
Fixed to the rack holder (57) by the rack shaft (20)
Only axial movement integral with is allowed. The rack holder (57) is integrally fastened to the rack shaft (20) with bolts (58) to connect the rack shaft (20) and the nut member (52) to the bolts (56), (56) and the bush (55). , (55) to allow the nut member (52) to move only in the axial direction integrally with the rack shaft (20). Above bush (55),
The (55) absorbs a bending moment acting on the rack shaft (20) due to a steering reaction force, and prevents an unnecessary load from being applied to the screw shaft (48) of the ball screw mechanism (53).

As shown in FIG. 6, the control device (62) has a control circuit (correction means, current value determination means) (63) and a motor drive circuit (energization means) (65). These control circuits (6
3) and motor drive circuit (65) are relay circuits (75)
And the in-vehicle battery power supply (7
2) and is supplied with power from the power source (72). The relay circuit (75) is connected to the key switch (74) and the control circuit (63) and driven by these to supply and cut off power.

The control circuit (63) is a microcomputer circuit (66),
A crystal oscillator circuit (67), an interface circuit (68) for the temperature sensor (60), an interface circuit (69) for the torque sensor (21), a constant voltage circuit (70), an amplifier circuit (71), etc. are mixed. There is. The temperature detection vibration signal (S ₃ ) is input from the temperature sensor (60) to the microcomputer circuit (66) via the interface circuit (68) and the steering torque sensor (21) to the steering torque via the interface circuit (69). The detection signals (S ₁ ) and (S ₂ ) are input, the signal (S ₄ ) is input from the amplifier circuit (71), and the reference clock signal (C) is input from the crystal oscillation circuit (67).
Is typing. The interface circuit (68) for the temperature sensor (60) has a resistance bridge circuit having the temperature sensor (60) as one resistance element and an amplifier circuit for amplifying the output of the bridge circuit. ), That is, a temperature detection signal (S ₃ ) representing the temperature (θ) is output. Interface circuit (69) for steering torque sensor (21)
Converts the reference pulse signal input from the microcomputer circuit (66) into an AC signal, and converts the reference pulse signal into 1 of the differential transformer (22).
It is supplied to the secondary coil (24), and also to the differential transformer (22).
The outputs of the secondary coil (25) and the tertiary coil are rectified and smoothed, and steering torque detection signals (S ₁ ) and (S ₂ ) indicating the direction and magnitude of the steering torque are output. The amplifier circuit (71) amplifies the output signal of the current detection circuit (80) of the electric motor drive circuit (65), which will be described later, and outputs a signal (S ₄ ) representing the current value being supplied to the electric motor (5), The constant voltage circuit (70) holds the electric power from the above-mentioned relay circuit (75) at a constant voltage and supplies it to each circuit. The microcomputer circuit (66) is composed of a memory, an arithmetic processing unit, etc., and each signal (S ₁ ), (S ₂ ), (S ₃ ), according to the program stored in the memory,
(S ₄ ) is processed to output a pulse width modulation control signal (PWM) signal (g), (h), (i), (j) to the motor drive circuit (6
Output to 5).

Motor drive circuit (65), gate drive circuit (77)
And four field effect transistors (FET) (Q ₁ ), (Q
_2), and (Q _3), (a bridge circuit having Q ₄₎ (78),
The booster circuit (76), the relay circuit (79), and the current detection circuit (80) are hybridized. The gate drive circuit (77) is applied with a voltage boosted at least twice the power supply voltage by the booster circuit (76), and the PWM signals (g), (h), which are input from the microcomputer circuit (66),
Each FET of the bridge circuit (78) based on (i) and (j)
Output a drive signal to. The bridge circuit (78) has a FET (Q
The drain terminals of ₁ ) and (Q ₄ ) are connected to the relay circuit (75), and the source terminals are connected to the drain terminals of FETs (Q ₂ ) and (Q ₃ ), respectively, and FETs (Q ₂ ) and (Q ₃ ) The source terminal of is connected to the-terminal of the power supply (72), and these FETs (Q ₁ ),
The electric motor (5) is connected between the source / drain terminal of (Q ₂ ) and the source / drain terminal of the FETs (Q ₄ ) and (Q ₃ ). This bridge circuit (78) consists of each FET (Q ₁ ),
A drive signal is input from the gate drive circuit (76) to the gates of (Q ₂ ), (Q ₃ ), (Q ₄ ), and FET (Q ₁ ), (Q ₃ ) or FET (Q ₂ ), (Q ₄ ) Is integrally and selectively driven ON to control the direction and value of the current flowing to the electric motor (5). In addition, the bridge circuit (78) of each PWM signal (g),
An intermittent current having an impact coefficient (duty factor) corresponding to (h), (i), and (j) is applied to the electric motor (5). Here, the PWM signal (g) is a signal corresponding to the impact coefficient of the FET (Q ₁ ), and similarly, the PWM signal (h) is the FET (Q ₄ ), PW
The M signal (i) is a signal corresponding to the impact coefficient of the FET (Q ₃ ) and the PWM signal (j) is a signal corresponding to the impact coefficient of the FET (Q ₂ ).

Relay circuit (79) is a microcomputer circuit (66)
Connected between the electric motor (5) and the bridge circuit (78) in accordance with the output signal of the micro-computer circuit (66), and the current detection circuit (80) is connected to the electric motor (5). The current value applied to the circuit is detected and a signal representing the current value is output to the amplifier circuit (71).

Next, the operation of this embodiment will be described with reference to FIG.

This electric motor type power steering apparatus controls the electric motor (5) by executing a series of processes shown in the flowchart of FIG. 7 in the microcomputer circuit (66).

First, when the ignition key is operated and the key switch (74) is turned on, electric power is supplied to the microcomputer circuit (66) and the like, and the microcomputer circuit (66) starts control (step P ₁ ). . Next step
In P _2, initialization of the microcomputer circuit (66) (initialization) is performed, erasing or the like of the stored data, such as internal register. Then, in step P ₃ ,
Initial failure diagnosis is performed according to another defined subroutine, and only when all functions are normal, proceed to step P ₄ .

In step P ₄ , the steering torque detection detection signals (S ₁ ) and (S ₂ ) are read, and the failure diagnosis of the steering torque sensor (21) is performed according to the subroutine defined elsewhere in step P ₅ . Only when the steering torque sensor in step P ₅ (21) are functioning properly, step P ₆
Go to. In step P ₆ , the signal value (S ₂ ) is subtracted from the signal value (S ₁ ) to obtain an internal signal T (hereinafter, referred to as steering torque T) indicating the steering torque. In the next step P ₇ , whether the steering torque T is positive or negative is determined. If the steering torque T is positive or 0, the flag F for displaying the steering direction is set to 0 in step P ₈ and the steering torque T is If the value is negative, the sign of the steering torque T is inverted in steps P ₉ and P ₁₀ , that is, the absolute value is set, and the flag is set to 1. In the following step P ₁₁ , the frictional resistance component DF (T) is retrieved from the data table 1 shown in FIG. 9 based on the steering torque T, and an internal signal indicating this is obtained (hereinafter referred to as the frictional resistance component DF (T)). And similarly in step P ₁₂ ,
The road surface load component DL (T) is searched from the data table 2 shown in FIG. 10 based on the steering torque T, and an internal signal indicating this is generated (hereinafter referred to as road surface load component DL (T)). The frictional resistance component DF (T) represents the frictional resistance of the steering force transmission system when the steering torque T acts, and similarly, the road surface load component DL (T) represents the road surface resistance during steering of the steered wheels. Represent

Next, in step P _13, reads the temperature detection signal (S _3), the failure diagnosis of the temperature sensor (60) is carried out in accordance with a subroutine defined in the other in the subsequent step P _14. Then, only when it is determined in this step P ₁₄ that the temperature sensor (60) is functioning normally, the step P ₁₅
Perform the following processing. In step P _15, a temperature detection signal (S
₃ ) is converted into an internal signal (hereinafter referred to as temperature θ) that displays the temperature θ in the case (17), and in the next step P ₁₆ , the temperature coefficient is calculated from the data table 3 shown in FIG. 11 based on the temperature θ. K (θ) is searched and an internal signal representing this (hereinafter referred to as temperature coefficient K (θ)) is generated. As is clear from FIG. 11, the temperature coefficient K (θ) takes a value of 1 in the range of the temperature from 0 to the predetermined value θ _1, but in the range where the temperature θ exceeds the predetermined value θ ₁ , the temperature θ It decreases with an increase of 0 and takes a value of 0 at a predetermined value θ ₂ . Then, step P
₁₇ , the road surface load component DL (T) and the temperature coefficient K (θ)
The road surface load component DL (T) is corrected by multiplying by and then, in step P ₁₈ , the corrected road surface load component DL (T) and the frictional resistance component DF (T) are added to correct the steering force. D (T) is calculated, and a signal representing the corrected steering force D (T) (hereinafter referred to as corrected steering force D (T)) is generated. This corrected steering force D
(T) is the PWM signal (g), (h),
The impact coefficients of (i) and (j) are displayed.

In the following step P ₁₉ , the value of the corrected steering force D (T) is determined, and if the corrected steering force D (T) is 0, the step P
_{At 20} , all the impact coefficients of the PWM signals (g), (h), (i), and (j) described above (for convenience, are represented by the same reference numerals as the signals; the same applies hereinafter) are set to 0, and the corrected steering force D ( if T) exceeds the 0 that correction steering force D (T) is more than 0 1 or less goes to step P _23. Step In P ₂₃ discriminates the value of the flag F, the step P ₂₄ If the flag F is at 0, P ₂₅ in the PWM signal (g), (h), (i),
Set the impact coefficient of (j) to 1,0, D (T), 0 respectively,
Further, PWM signal in step P _26, P ₂₇ If the flag F is at 1 (g), (h) , the duty cycle of (i), (j), respectively
Set to 0,1,0, D (T). And in the next step P ₂₁
The PWM signals (g), (h), (i), (j) are output to the motor drive circuit (65). Thereafter, in step P _22, performs a failure diagnosis of the electric motor (5) based on the output signal of the current detection circuit (80) (S _4), again step only when the electric motor (5) is functioning normally A series of processing from P ₄ is repeated.

As described above, in the electric power steering apparatus according to the present embodiment, the road surface load component DL (T) of the steering force T is corrected according to the temperature θ of the transmission system to reduce it at high temperature of the transmission system. Based on the corrected steering force, the value of current flowing to the electric motor (5) is controlled. Therefore, at a high temperature of the transmission system, it is possible to suppress heat generation in the electric motor (5) and the drive circuit (65) without deteriorating the steering feeling, and reduce the thermal influence on the electric motor (5) and other devices. You can Then, the transmission system temperature θ is the above-mentioned predetermined temperature θ
Even when the temperature exceeds ₂ , the electric motor (5) generates an auxiliary force corresponding to the frictional resistance component in the transmission system, so that steering such as emergency avoidance can be reliably performed.

Next, another embodiment of the present invention will be described based on the flowchart of FIG. In the following, only the parts (steps P _{11 to} P ₁₉ ) different from the previous embodiment will be described, and description of the other parts will be omitted.

In this embodiment, in step P ₁₁ , the road surface load component is calculated based on the steering torque T from the data table 2 shown in FIG.
Find the DL (T), followed by the temperature detection signal in step P ₁₂ (S
₃₎ Load the failure diagnosis of the temperature sensor (60) is performed in step P _13. In the next step P ₁₄ , the temperature detection signal (S ₃ ) is converted into the temperature θ, and in step P ₁₅ , the first
Temperature coefficient K based on temperature θ from data table 3 in Fig. 1
Search for (θ).

In step P ₁₆ , the road surface load component DL (T) is multiplied by the temperature coefficient K (θ) to correct the road surface load component DL (T). Then, in step P ₁₇ , the frictional resistance component DF (θ) is retrieved from the data table 4 shown in FIG. 12 based on the temperature θ. This frictional resistance component DF (θ) represents the frictional resistance force of the transmission system unrelated to the steering force T, that is, the frictional resistance of the sliding portion of the mechanical portion of the transmission system which is affected by the viscosity of the lubricating oil. As is clear from the above, the temperature is set to be large in the low temperature region. Then step P ₁₈
In the steering torque T, it is determined whether or not more than the value A for determining the dead zone, the steering torque T advances to step P ₁₉ equal to or greater than the value A, if the road load component DL (T) is smaller than the value A step After the frictional resistance component DF (θ) is set to 0 at P ₂₀ , the process proceeds to step P ₁₉ . In Step P ₁₉ , as described in the previous embodiment, the corrected road surface load component DL
(T) and the frictional resistance component DF (theta) and the addition to calculating the corrected steering force D (T), after the step P ₂₁ the corrected steering force D (T) of the PWM signal in the subsequent processing (i) , (J) of the impact coefficient.

In this electric power steering system, the frictional resistance component DF (θ) is obtained when the temperature θ is low, that is, when the viscosity of the lubricating oil that lubricates the sliding parts of the mechanical components of the transmission system is high and the frictional resistance is large.
Becomes larger, the auxiliary force generated by the electric motor (5) also becomes larger, the influence of the viscosity of the lubricating oil due to the temperature change can be eliminated, and a constant steering feeling can be obtained regardless of the temperature θ. And when the temperature θ is high,
Since the frictional resistance component DF (θ) becomes small, the current value supplied to the electric motor (5) is suppressed as in the previous embodiment, and the heat generation of the electric motor (5) and the like becomes small, so that the equipment can be protected. It will be possible.

(Effects of the Invention) As described above, according to the electric power steering apparatus of the present invention, the steering force acting on the steering force transmission system is corrected by the temperature of the transmission system, and the corrected steering force is corrected. Based on the above, an auxiliary force corresponding to the frictional resistance component of the transmission system is secured, and the current supplied to the electric motor is controlled so as to be small when the temperature of the transmission system is high. Therefore, the amount of heat generated by the electric motor can be reduced without losing the steering force-dependent characteristics of the auxiliary force generated by the electric motor.
It becomes possible to protect the electric motor and the like from heat without deteriorating the steering feeling, and moreover, it becomes possible to reliably carry out steering during emergency avoidance.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an electric motor type power steering apparatus of the present invention. 2 to 7 show an electric motor type power steering apparatus according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view, FIG. 3 is a sectional view taken along the line III-III in FIG. Figure 4 is IV- in Figure 2.
A sectional view taken along the line IV, FIG. 5 is a sectional view taken along the line VV of FIG. 2, FIG. 6 is a block diagram of the electric circuit, and FIG. 7 is a flowchart of the control process. FIG. 8 is a flowchart showing the control processing of the electric motor type power steering apparatus according to another embodiment of the present invention. FIG. 9, FIG. 10, FIG. 11 and FIG. 12 show data tables used for the control processing of each embodiment. 5 ... Electric motor 21 ... Steering torque sensor (steering force detection means) 60 ... Temperature sensor (temperature detection means) 62 ... Control device 63 ... Control circuit (correction means, current value determination means) 65 ... Electric motor drive Circuit (energizing means)

Claims (1)

[Claims] 1. A steering force transmission system is provided with an electric motor for generating a steering assist force, and the amount of electric power supplied to the electric motor is at least the steering force detection means for detecting the steering force of the transmission system and the temperature of the transmission system. In a motor-driven power steering apparatus that controls based on an output signal of a temperature detecting unit that detects, a steering force detected by the steering force detecting unit is corrected based on a temperature detected by the temperature detecting unit to obtain a corrected steering force. Correction means for determining, and a current value determination means for determining a target current value that secures an auxiliary force corresponding to a frictional resistance component of the transmission system at least at high temperature based on the corrected steering force determined by the correction means, An electric motor type power steering apparatus comprising: an electric current supplying means for supplying a current having the target current value to the electric motor based on an output signal of the electric current value determining means. The correction means calculates a road surface load component of the steering force based on an output signal of the steering force detection means, and a road surface load determination means based on an output signal of at least one of the steering force detection means and the temperature detection means. A frictional resistance determining means for calculating the frictional resistance component of the steering force by the transmission system; a temperature coefficient determining means for setting a temperature coefficient according to the temperature of the transmission system based on an output signal of the temperature detecting means; Road surface load correction means for calculating a corrected road surface load component by multiplying the road surface load component by the temperature coefficient based on the output signals of the count determination means and the road surface load determination means, and the road surface load correction means and the frictional resistance determination means. And a corrected steering force calculation means for calculating the corrected steering force by adding the frictional resistance component and the corrected road surface load component based on the output signal of Motor power steering apparatus ranging first claim of claims to symptoms.